The present invention relates to a data processing semiconductor device, and particularly to a technology that can be effectively applied to a data processing semiconductor device having a built-in rewritable nonvolatile memory.
Recently, microcomputer products having rewritable nonvolatile memories mounted thereon for use in controlling car engines or the like are required to operate at higher temperatures. However, since repeated overwriting in an ultra-high temperature environment may degrade the retention property of flash memories mounted on microcomputers as rewritable nonvolatile memories, thereby failing to perform normal writing or erasing, it is necessary to limit overwriting at a high temperature.
As prior art, Japanese Patent Laid-Open No. 2002-367382 (Patent Document 1) discloses the technology of improving the reliability when reading data, based on reduced margin of the guaranteed voltage due to temperature variation.
The method described in Patent Document 1 attempts to improve data reliability by detecting the temperature of a semiconductor integrated circuit having a flash ROM (Read Only Memory) mounted thereon and, based on the detected temperature, adjusting the pulse width or voltage level of writing or erasing pulses applied to a memory cell when overwriting the flash ROM.
The inventors consider that the method described in the above-mentioned Patent Document 1 requires a large-scale control circuit for adjusting the pulse width and voltage level of writing or erasing pulses based on temperature. In addition, there is limitation in improving disturb resistance and retention property in an ultra-high temperature environment although writing or erasing is performed by the control.
The present invention has been made in view of the above circumstances and improves the reliability of controlling overwriting of a nonvolatile memory in a data processing semiconductor device.
The other purposes and the new feature of the present invention will become clear from the description of the present specification and the accompanying drawings.